Properties of Alcohols
Specification Reference 4.2.1 (a)
Quick Notes
- Alcohols are organic compounds with an –OH (hydroxyl) group.
- Alcohols are polar due to the O–H bond, which allows hydrogen bonding between molecules.
- This gives them higher boiling points and better water solubility than alkanes.
- Alcohols are classified as:
- Primary (1°): OH on a carbon bonded to 1 alkyl group
- Secondary (2°): OH on a carbon bonded to 2 alkyl groups
- Tertiary (3°): OH on a carbon bonded to 3 alkyl groups
Full Notes
Alcohols are organic compounds with a hydroxy (–OH) group.
They are polar molecules due to the large difference in electronegativity of the oxygen and hydrogen atoms in the O–H bond group.
This polarity allows alcohols to form hydrogen bonds with water and with other alcohol molecules.
As a result:
- Alcohols have relatively high boiling points compared to alkanes of similar mass.
- They are soluble in water, especially the shorter-chain alcohols.
Matt’s exam tip
Remember when drawing hydrogen bonds between molecules to make a clear 180° angle between the O–H···O and show all dipoles and lone pairs of electrons.
Classification of Alcohols
Alcohols are classified by the number of carbon atoms attached to the carbon bonded to the –OH group:
- Primary alcohol (1°): OH group on a carbon bonded to one other carbon
- Secondary alcohol (2°): OH on a carbon bonded to two other carbons
- Tertiary alcohol (3°): OH on a carbon bonded to three other carbons
This classification is important for predicting reaction outcomes.
Summary
- Alcohols are polar molecules due to the O–H bond and can form hydrogen bonds.
- They have higher boiling points and solubility than alkanes.
- Alcohols are classified as primary, secondary, or tertiary depending on the number of carbons bonded to the OH carbon.